Internal combustion engine equipped with means for reducing the amount of nitrogen oxide which is exhausted from the engine

ABSTRACT

An internal combustion engine for vehicles equipped with means for reducing harmful exhaust gases, especially nitrogen oxide, in which a first ignition plug and a second ignition plug are so installed in the combustion space of the engine that the combustion characteristic of the first plug is superior to that of the second plug. Either or both of these plugs are differently operated in accordance with the nitrogen oxide content in the exhaust gas.

United States Patent [1 1 Hosho et a].

[111 3,809,042 [451 May 7, 1974 INTERNAL COMBUSTION ENGINE EQUIPPED WITHMEANS FOR REDUCING THE AMOUNT OF NITROGEN OXIDE WHICH IS EXHAUSTED FROMTHE ENGINE Inventors: Yukio Hosho; Hisanori Moriya, both of Katsuta;Yoshishige Oyama, Hitachi, all of Japan Assignee: Hitachi, Ltd., Tokyo,Japan Filed: Apr. 22, 1971 Appl. No.: 136,529

Foreign Application Priority Data Apr. 22, 1970 Japan 45-33899 June 26,1970 Japan 45-55162 US. Cl..... 123/148 C, 123/148 DS, 123/148 E Int.Cl. F02p 3/06 Field of Search 123/148 C, 8.09, 191 S,

References Cited UNITED STATES PATENTS 6/1953 Saunders 123/148 C2,025,203 12/1935 Harper 123/148 C 3,584,608 6/1971 Shibagaki...2,025,202 12/1935 Harper 1,580,353 4/1926 Vincent 3,452,725 7/1969 Kelly3,534,717 10/1970 Froede 123/148 C FOREIGN PATENTS OR APPLICATIONS612,150 1/1961 Canada 123/191 S Primary Examiner-Laurence M. GoodridgeAssistant Examiner-C. Flint Attorney, Agent, or FirmCraig and AntonelliABSTRACT 9 Claims, 11 Drawing Figures PATENTEDIAY 11914 3.809.042 SHEET1 OF 3 INVENTOR. YIJKIO Hosno, HISANORI Mom A A HOSHISHIGE oYAMA amwnm'(la-+3.12

A'ITOR'N EYS PAIENTEDIAY 1 m4 3.809.042

sum 2 or 3 2.000 NOX |,ooo

500 H PPM NO 2 3 4 5 e FIG. 5b CO NO 2 s 4 5 e 400 Fl 50 HC PPM 7INVENTOR. YUKIO HOSHO, HISANORI M ORIYA and YOSHISH [6E OYA HA ATTORNEYSI INTERNAL COMBUSTION ENGINE EQUIPPED WITH MEANS FOR REDUCING THE AMOUNTOF NITROGEN OXIDE WHICH IS EXHAUSTED FROM THE ENGINE BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to aninternal combustion engine equipped with means for reducing the nitrogenoxide content in the exhaust gas thereof without increasing the amountof other harmful substances, such as carbon monoxide and hydrocarbons.

2. Description of the Prior Art The problem of air pollution owing to anextraordinary increase in the number of automotive vehicles in citytraffic has become a big social problem everywhere in the world; as aresult, it has been decided to restrict the contents, not only ofhydrocarbons and carbon monoxide in the exhaust gases, but also ofnitrogen oxide (NO,) because of the formation of smog by thephotochemical reaction in the air and of its stimulative affectation ofthe eyes of human beings.

Incidentally, as is known, the production of the hydrocarbons and carbonmonoxide takes place due to an insufficiency of combustion in thecylinders of the engine and, therefore, it is possible to considerablydecrease the amounts of these components when the combustion is carriedout completely by providing a sufficient amount of air at hightemperatures, and this improvement in combustion efficiency causes anincrease in the thermal effect of the engine.

In contrast thereto, since a lowering of the maximum combustiontemperature has a tendency to suppress an increase of the combustionefficiency of the engine to prevent, as a result thereof, the formationof of nitrogen oxide in the exhaust gas, the following measures havebeen proposed heretofore as solution to the above problems:

I. controlling the spark advance;

2. providing such a mixture gas as avoids the peak air-fuel ratio;

3. recycling a part of the exhaust gas;

4. injecting water; and

5. employing a catalytic converter.

The above systems, however, are not yet practicable because they involvedifferent problems. That is, in the case of changing the spark advance,the tendencies of a decrease in the output power and of an increase inthe fuel cost in proportion to the reduction in the rate of nitrogenoxide are great and, furthermore, the value of the decrease in nitrogenoxide can not be made as large as is desired because the angle throughwhich a change can be effected is limited at most to In the system ofchanging the mixing ratio of air-fuel, when the gas mixture isrelatively thin or lean, an ignition failure takes place frequentlycausing an instability of the number of revolutions of the engine,whereas, to the contrary, when the gas mixture is relatively rich, thecontents of hydrocarbons and carbon monoxide in the exhaust gases-becomelarge and the fuel cost increases.

In the system of recycling the exhaust gas in which a part of theexhaust gas is subjected to reintroduction into the engine by thesuction effect of the latter, the I ignition becomes unstable due to thepresence of the uncombusted substances and, furthermore, carbon ortar-like substances tend to be deposited in the suction pipe, suctionvane, etc. Furthermore, in the water injection system, it is necessaryto use as much water as fuel, and the apparatus for controlling theamount of water increases the cost of the vehicle. Finally, a catalyticsystem satisfying the desired purifying ability and the required servicelife has not been developed.

Among the above-mentioned systems, the system for recycling the exhaustgas is rather useful in view of the rate of decreasing the amount ofnitrogen oxide and of the small decrease in the output loss, and such adevice combined with both the mixing-ratio-changing system and theignition-control system is therefore believed at present to be mostavailable and practicable. In such a system, however, the drawbacksinvolved in the recycling system necessarily remain. The foregoingdescribes the present condition in connection with the measuresinvolving the nitrogen oxide problem.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a system for reducing the nitrogen oxide content in the exhaustgases of an internal combustion engine without increasing the amount ofother harmful substances.

It is another object of the present invention to provide an internalcombustion engine equipped with a system for remarkably reducing theamount of nitrogen oxide in the exhaust gas without increasing a loss ofoutput power.

It is still another object of the present invention to provide such anapparatus for reducing nitrogen oxide as will produce no increase oronly an extremely small increase in the contents of hydrocarbons andcarbon monoxide in spite of a large decrease in the content of nitrogenoxide in the exhaust gas, so that all the problems owing to theabove-mentioned harmful substances can be solved in an effective manner.

It is still another object of the present invention to provide a systemfor reducing the harmful substances in the exhaust gases substantiallywithout any contamination within the engine.

It is a still further object of the present invention to provide aninternal combustion engine equipped with such a nitrogen-oxide-reducingsystem as will not deteriorate the operation of the engine.

The present invention provides an internal combustion engine equippedwith a system for reducing or suppressing the production of nitrogenoxide as well as for exhausting hydrocarbons and carbon monoxide, inwhich a combustion chamber is provided with a pair of ignition plugsdifferent from each other with respect to their combustioncharacteristics, each of both of them being operated in accordance withthe condition of the engine operation, whereby the nitrogen oxidecontent in the exhaust gas is reduced.

The foregoing objects as well as other objects, features and advantagesof the present invention will become apparent from the followingdetailed description, taken in conjunction with the attached drawings,in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of a cylinderhead embodying the present invention;

FIG. 2 is a vertical cross-sectional view of a cylinder embodying thepresent invention;

FIG. 3 is a vertical cross-sectional view of the important portion ofthe cylinder shown in FIG. 2;

FIG. 4 is a circuit diagram for an ignition device according to thepresent invention;

FIGS. 5a to 5c are graphs, respectively showing the content of nitrogenoxide, carbon monoxide and hydrocarbons in the exhaust gas fromconventional engines of the prior art and from engines according to thisinvention, which are operated continuously;

FIGS. 6a to 60 are graphs, respectively showing the content of nitrogenoxide, carbon monoxide and hydrocarbons in the exhaust gas fromconventional engines of the prior art and from engines according to thisinvention, which are operated under various conditions;

and

FIG. 7 is a circuit diagram of another embodiment of thepresent'invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1 to 4,a cylinder head 1 is provided with a pair of ignition plugs 3, 4, anintakevalve 5 and an exhaust valve 6. The ignition plugs 3, 4 aredisposed within a combustion space 2 to ignite'the fuel which is presenttherein. A piston 7 connected through a suitable'connecting means, suchas a crank means, to shafts of distributors 9, 10, reciprocates in acylinder.

The ignition'plug 3, an ignition coil 11 and the distributor 9constituting a first ignition means generally designated by referencenumeral 12, and the ignition plug 4, an ignition coil 14 and thedistributor constituting a second ignition means generally designated byreference numeral 15, each include a respective condenser 16, 17, whichare alternately connected through a conventional change-over switch 18to a battery 19 (FIG. 4). In the first ignition means 12 an ignitionportion 20 of an electrode of the ignition plug 3 projects into thecombustion space 2 ma conventional manner, whereas, in' contrastthereto, the ignition plug 4 is placed within a recess 23 formed in acylinder wall 22 so as not to project with the ignition portion 21 of anelectrode of the ignition plug 4 into the combustion space 2. V

In the above construction, under operating conditions as will cause theamounts of nitrogen oxide in the exhaust gases to be large, for example,in the case of a small-load, high-speed operation or of an accelerationoperation, only the second ignition means is operated. In the otheroperating conditions, only the first ignition means 12 or both ignitionmeans are operated. Since the control of the spark plugs 3 and 4 in themanner described above can be achieved by conventional means responsiveto load and/or speed or acceleration, a detailed description thereof isdispensed with herein, especially as the engine parameters, such asvacuum in the intake manifold, etc., are known to those skilled in theart, which can be used as control magnitudes.

The volume and shape of the recess 23, in which the ignition plug 4 ofthe second ignition means is disposed, are properly determined andchosen in accordance with experiments; in any case the combustioncharacteristics of the second ignition means 15, i.e., the combustioncharacteristics that are imparted by the ignition means 15 including itsignition plug 4 to the gas mixture in the combustion space 2, must bemade inferior to those of the first ignition means 12. For example, sucha relationship between the two ignition means 12 and 15 is realized thatthe flame propagation speed, which is the speed of the flame propagationfrom the position of the electrode 21 of the ignition plug 4 over theentire combustion space '2, is made smaller than the speed obtained withthe first ignition means 12. The above relationship is established bytaking into consideration the desirability not to excessively increasethe contents of carbon monoxide and hydrocarbons in the exhaust gasesand not to lower the output power of engine.

Various ways and means of conventional nature exist which permit todetermine the correct ignition times for the two ignition means 12 and15, i.e., the operating condition of the change-over switch 18, takinginto due consideration the running condition in city traffic, where thecongestion of traffic is heavy, and the running condition in thecountry, where the exhaust gases do not represent as severe a trouble asin city traffic, or such items as stability of engine rotation,fuel-cost efficiency and output power, etc. For example, the ignitiontime can be decided by detecting the opening degree of a throttle valveand/or the back pressure, and/or by using the changing in thetransmission and/or by adding the temperature condition of the engine toany of the foregoing parameters. As stated above, the ignition timecondition is thus chosen by conventional means in accordance with theconditions of exhaust gas restrictions. Since switches 18 performingthese functions are known in the art and are available, a detaileddescription thereof is also dispensed with herein. The analyticalresults of the exhaust gas contents are shown in FIGS. 5a through 6c, inwhich an engine embodying the present invention has a capacity of 1,200cubic centimeters.

In FIGS. 5a through 60, data Nos. 1 and 2 show the results in connectionwith the engines provided with the same ignition means. In FIGS. 5a to50, data No. 1 relates to such engines as are of the ordinary type withrespect to the diameter of the main jet of the evaporator, the positionof the ignition plug and the spark advance, which corresponds to thefirst ignition means according to the present invention. On thecontrary, data No. 2 relates to an ignition means in which the portionof the electrode 21 of the ignition plug 4 is recessed by millimeters ascompared with the conventional one, i.e., this arrangement of theignition means corresponds to the second ignition means 15.

In the case of data Nos. 3 and 5, only the diameter of the main jet ofthe evaporator is changed as compared with that of the engine of dataNo. 1; in the case of data No. 4, the position of the ignition plug asused in data No. 3 is changed, and in the case of data No. 6, theposition of the ignition plug of that of data No. 5 is changed and theignition time is delayed by 10 degrees in angle as compared with that ofdata No. 5.

According to FIGS. 50 to 50, it will be appreciated that a considerablereduction of the nitrogen oxide amount is attained and, furthermore, bycombining the second ignition means with such changes as changes of thediameter of the main jet and the spark advance, it is possible toremarkably reduce the amount of nitrogen oxide. According to the presentinvention, the amounts of carbon monoxide and hydrocarbons do not changeunfavorably, but rather decrease.

In the conventional systems, if the amount of nitrogen oxide isdecreased, there exists a tendency for the amount of other harmfulcomponents to become remarkably large; however, there is no suchundesirable relationship in the present invention.

. substances can There are shown in FIGS. 6a to 6c the analyticalresults of the amounts of nitrogen oxide, carbon monoxide andhydrocarbons in the exhaust gas, in which the tests were performed bychanging the running conditions of the vehicle. According to FIGS. 6a to6c, the largest amount of nitrogen oxide is found in the accelerationrun, and it is appreciated that the reduction of the amount of nitrogenoxide is considerable when the present invention is employed. Inconnection with the amounts of carbon monoxide and hydrocarbons, a smallchange of the amount of carbon monoxide is produced, and the amount ofhydrocarbons seems to become slightly larger. However, the amounts ofthese means and in any conventional manner, such as, for example, byblowing air for recombustion into an exhaust pipe. Thus, it is possibleto reduce the amounts of nitrogen oxide, hydrocarbons and carbonmonoxide to operate the second ignition means during accelerationrunning conditions and to operate the first ignition means during otherrunning conditions. It is, of course, possible for effecting thereduction of nitrogen oxide in the operation other than the accelerationto determine the position of the ignition plug, the shape of the recessor the like of the second'ignition means.

In FIGS. 6a to 60, the running conditions are as follows:

I: idling II: acceleration running (0 25 mile/hr.)

lll: constant running (30 mile/hr.)

IV: deceleration running (30 mile/hr.)

V: constant running (15 mile/hr.)

VI: acceleration running (15 30 mile/hr.)

VII: deceleration running (50 mile/hr.)

In another example, both the first and second ignition means are usedduring the normal running condition, but when the amount of nitrogenoxide is undesirably large, only the second ignition means is operated,whereby the efficiency of engine during the high speed running can beincreased.

According to the present invention, the first and second ignition meanscan be so modified as to be capable of producing a' proper engineefficiency during the normal running operation by means of the twoignition means and capable of allowing only the second ignition means tooperate at the time when the amount of nitrogen oxide is undesirablylarge. Furthermore, it is possible to delay the spark advance so as tooperate only the second ignition means when the amount of nitrogen oxideis large. The objects of the present invention are attained by using asingle distributor which is operatively connected to both the first andsecond ignition means in which the spark advances of respective ignitionmeans are so regulated as to function properly themselves.

In the following example, a distributor is connected to a pair of rotaryelectrodes and a pair of ignition plugs are provided with fixedelectrodes. Only the first ignition plug, which is fixed as in theordinary case, is allowed to make and break by means of a suitableswitch connected to the source.

In FIG. 7, a battery 109 is connected by way of con tactors 110, 111 andcoils 112, 113 to rotary contacts of electrodes 114, 115. Between thebattery 109 and the coil 112 for the main plug are inserted differentswitches such as, for example, a throttle valve switch 132 .which isoperated in accordance with the opening be easily reduced by anysuitable of the throttle valve, a speed switch 133 which is operated inaccordance with the vehicle speed, a gear switch 134 which is changedover in accordance with the selected speed or gear position.

Fixed contacts or electrodes 116, 117, 118 and 119 are provided on theside of the main plugs, which respectively cooperate with the rotarycontact or electrode 114 and are connected to the main plugs 120, I21,122 and 123, respectively, of the engine cylinders. Fixed contacts orelectrodes 124, 125, 126 and 127 are provided on the side of auxiliaryplugs which respectively cooperate with the rotary contact or electrode115 and are connected to auxiliary plugs 128, 129, 130 and 131,respectively. The rotary contacts or electrodes 114'and 115 are drivenby a crank shaft.

According to the above-described construction, it is possible toenergize both the main and auxiliary plugs or only each of the plugs bymeans of the single distributor. Selection of the switches to beoperated is made in accordance with the characteristics of engine, theregulations of exhaust gas restriction, or other conditions. Forexample, in the case of the idling operation in which the opening of thethrottle valve and the mixing ratio of fuel to air is small or in casethat the opening of the throttle valve is large and a large output poweris necessary, the throttle switch 132 for detecting the opening of thethrottle valve is used in order to operate both the main plug 3 and theauxiliary plug 4. In the case of a high speed operation, in which it isrequired to prevent a decrease in the amount of fuel consumption, thegear switch 134 which is operatively connected to the change-speed-gearsystem is used. In the case of the speed acceleration, the speed switch133 and gear switch 134 are used by detecting the acceleration conditionso as to operate only the auxiliary plug.

Further, in the case of operating the vehicle in the country where theair pollution is not as severe a problem as in city traffic, only themain plugs 3 are operated.

According to the above-described embodiments of the present invention,it is possible to greatly reduce the amount of nitrogen oxide withoutincreasing the amounts of other harmful substances such as carbonmonoxide and hydrocarbons in a reduced size system, while theconventional systems are difficult to employ in practice because theyhave technical or economical drawbacks.

It goes without saying that the recess for accommodating the auxiliaryplug therein can be replaced by other means, such as by using such anignition plug as has a cylindrical cover surrounding the end of theelectrode and the vicinity thereof.

Although we have described specific preferred embodiments of the presentinvention, it is understood that the scope of the present invention isnot limited thereto, but is susceptible of numerous changes andmodifications as are known to those skilled in the art, and we thereforeintend to cover all such changes and modifications as are encompassed bythe scope of the appended claims.

What we claim is:

1. An internal combustion engine equipped with means for reducing theamount of nitrogen oxide in the exhaust gases thereof, withoutincreasing other harmful substances such as carbon monoxide andhydrocarbons, characterized in that said means comprises first ignitionmeans and second ignition means, said two ignition means beingoperatively connected to means for changing the ignition thereof, saidsecond ignition means being disposed in a recess communicating with acombustion space so that the combustion characteristics of said secondignition means is inferior to those of said first ignition means inorder to carry out the combustion by said second ignition means at arelatively smaller rate than that in the case of said first ignitionmeans, but to carry out the full combustion so as not to increase theamounts of carbon monoxide and hydrocarbons in the exhaust gases, saidchanging means operating only said second ignition means foracceleration and high speed operation of the engine such that thecombustion at the time of acceleration and high speed operation iseffected only by said second ignition means.

2. An internal combustion engine according to claim 1, in which acylinder wall of the engine is provided with'said recess foraccommodating an ignition plug of said second ignition means, anelectrode head of said plug being retracted as compared to the normalposition thereof so as to impart poor combustion characteristics to saidsecond ignition means, and the position of an ignition plug of saidfirst ignition means being located in the normal position.

3. An internal combustion engine according to claim 1, in which saidchanging means includes means for changing over said first and secondignition means in accordance with instructions for reducing the amountof nitrogen oxide.

' 4. An internal combustion engine according to claim 1, in which saidfirst and second ignition means are so arranged that they are operatedduring the normal running of vehicle until an instruction for reducingthe amount of nitrogen oxide and affecting the ignition of said secondignition means is given to said changing means. 7

5. An internal combustion engine according to claim 1, in which each ofsaid first and second ignition means is provided with means foradvancing the ignition.

6. An internal combustion engine equipped with means for reducing theamount of nitrogen oxide in the exhaust gases of a vehicle, in which acombustion space of an engine is provided with a main ignition plug andan auxiliary plug, said main ignition plug being located in such'a placewhere the combustion characteristics and thermal efficiency are superiorto those of other places, said auxiliary ignition plug being disposed ina recess of the engine communicating with said combustion space so thatthe speed of flame propagation after the ignition is smaller than thatof said main ignition plug, said ignition plugs being respectivelyconnected to a single distributor means which has a pair of rotaryelectrodes and a pair of fixed electrodes, said main ignition plug andsaid auxiliary plug being operated by relay means, said relay meansoperating only said auxiliary plug for acceleration and high speedoperation of the engine whereby the amount of nirogen oxide is properlyreduced without excessively increasing the amounts of carbon monoxideand hydrocarbons during all of the running conditions of vehicle.

7. An internal combustion engine equipped with means for reducing theamount of nitrogen oxide in the exhaust gases thereof withoutsubstantially affecting the amounts of other harmful components,comprising at least one combustion chamber, first and second ignitionmeans for each combustion space, said first and second ignition meansproviding different combustion characteristics for the fuel-air mixturein the combustion space, said second ignition means including anignition plug disposed in a recess of the engine communicating with saidcombustion space so that the speed of flame propagation after theignition is smaller than that of said first ignition means and controlmeans operatively connected with said ignition means for controlling theoperation thereof as a function of engine parameters affecting thecontents of nitrogen oxide in the exhaust gases, said control meansoperating only said second ignition means for acceleration and highspeed operation of said engine.

8. An internal combustion engine according to claim 1, wherein saidengine includes at least one cylinder and a piston disposed therein, andsaid first and second sive to the running condition of the vehicle.

1. An internal combustion engine equipped with means for reducing theamount of nitrogen oxide in the exhaust gases thereof, withoutincreasing other harmful substances such as carbon monoxide andhydrocarbons, characterized in that said means comprises first ignitionmeans and second ignition means, said two ignition means beingoperatively connected to means for changing the ignition thereof, saidsecond ignition means being disposed in a recess communicating with acombustion space so that the combustion characteristics of said secondignition means is inferior to those of said first ignition means inorder to carry out the combustion by said second ignition means at arelatively smaller rate than that in the case of said first ignitionmeans, but to carry out the full combustion so as not to increase theamounts of carbon monoxide and hydrocarbons in the exhaust gases, saidchanging means operating only said second ignition means foracceleration and high speed operation of the engine such that thecombustion at the time of acceleration and high speed operation iseffected only by said second ignition means.
 2. An internal combustionengine according to claim 1, in which a cylinder wall of the engine isprovided with said recess for accommodating an ignition plug of saidsecond ignition means, an electrode head of said plug being retracted ascompared to the normal position thereof so as to impart poor combustioncharacteristics to said second ignition means, and the position of anignition plug of said first ignition means being located in the normalposition.
 3. An internal combustion engine according to claim 1, inwhich said changing means includes means for changing over said firstand second ignition means in accordance with instructions for reducingthe amount of nitrogen oxide.
 4. An internal combustion engine accordingto claim 1, in which said first and second ignition means are soarranged that they are operated during the normal running of vehicleuntil an instruction for reducing the amount of nitrogen oxide andaffecting the ignition of said second ignition means is given to saidchanging means.
 5. An internal combustion engine according to claim 1,in which each of said first and second ignition means is provided withmeans for advancing the ignition.
 6. An internal combustion engineequipped with means for reducing the amount of nitrogen oxide in theexhaust gases of a vehicle, in which a combustion space of an engine isprovided with a main ignition plug and an auxiliary plug, said mainignition plug being located in such a place where the combustioncharacteristics and thermal efficiency are superior to those of otherplaces, said auxiliary ignition plug being disposed in a recess of theengine communicating with said combustion space so that the speed offlame propagation after the ignition is smaller than that of said mainignition plug, said ignition plugs being respectively connected to asingle distributor means which has a pair of rotary electrodes and apair of fixed electrodes, said main ignition plug and said auxiliaryplug being operated by relay means, said relay means operating only saidauxiliary plug for acceleration and high speed operation of the enginewhereby the amount of nirogen oxide is properly reduced withoutexcessively increasing the amounts of carbon monoxide and hydrocarbonsduring all of the running conditions of vehicle.
 7. An internalcombustion engine equipped with means for reducing the amount ofnitrogen oxide in the exhaust gases thereof without substantiallyaffecting the amounts of other harmful components, comprising at leastone combustion chamber, first and second ignition means for eachcombustion space, said first and second ignition means providingdifferent combustion characteristics for the fuel-air mixture in thecombustion space, said second ignition means including an ignition plugdisposed in a recess of the engine communicating with said combustionspace so that the speed of flame propagation after the ignition issmaller than that of said first ignition means and control meansoperatively connected with said ignition means for controlling theoperation thereof as a function of engine parameters affecting thecontents of nitrogen oxide in the exhaust gases, said control meansoperating only said second ignition means for acceleration and highspeed operation of said engine.
 8. An internal combustion engineaccording to claim 1, wherein said engine includes at least one cylinderand a piston disposed therein, and said first and second ignition meansincludes respectively first and second ignition plugs, said firstignition plug being disposed in the combustion space and second ignitionplug being disposed in said recess in said cylinder wall.
 9. An internalcombustion engine according to claim 1, wherein said changing meansincludes means responsive to the running condition of the vehicle.